Clearly you are unlikely to need 70li, but you might need more than you think by the time you have the warm and protective clothing and equipment you might think is required to be safe in all the conditions you could reasonably expect to meet.
I have a friend preparing to walk in Nov/Dec this year after having completed the CF twice before in mid and early spring. He is carrying some extra equipment items he didn't carry on his previous camino, such as an emergency blanket and GPS, while other items will be heavier, such as outer clothing and wet-weather gear. He is currently planning on using a 60li pack.
Given your relative sizes, I would expect this would be the equivalent of 50li for you, and the load would weigh about 10-11kg. With water, a day's food and your pack, this would give a total pack weight of around 15kg. If you are wearing 2.5-3kg of gear, your from the skin out load would be around 18kg, or 30% of your lower body mass.
Carrying 30% of your body mass is generally considered the upper limit for comfortable long distance hiking. It will slow you down. My own experience that is that at this size load, I am perhaps 40% slower than if I am carrying a 20% load. At 20% I average about 5kph or a little more. At 30% I average around 3kph. It makes for longer walking days for the same daily walking targets, and you will be doing this in winter, when you will be facing shorter daylight hours as well.
A winter camino, like any other outdoors activity in winter, is substantially different to doing the same thing in summer - a substantially more challenging undertaking.
BTW, it is possible to get closer to 20% FSO in winter. You might need to be prepared to be a little less comfortable, as well as get really good lightweight clothing and equipment. You might shave a kilogram or so of your base weight with judicious lightweight clothing choices, but the big difference would be to get a much lighter pack. If that isn't where you want to go, then you can expect to be a bit slower during the day, and make your daily plans accordingly.
Regards,